docs: def split_files(files, split_train, split_val, use_test):
      """Splits the files along the provided indices
      """
      files_train = files[:split_train]
      files_val = files[split_train:split_val] if use_test else files[split_train:]
  
      li = [(files_train, 'train'), (files_val, 'val')]
  
      # optional test folder
      if use_test:
          files_test = files[split_val:]
          li.append((files_test, 'test'))
      return li